1. Field of the Invention
The present invention relates to zoom lens systems and more particularly to a compact zoom lens system with a small aperture which projects on a screen or the like in an enlarged manner an image formed by changing a reflective direction of light from a light source such as a DMD.
2. Description of the Related Art
A projector that employs a DMD as a light bulb has been considered as advantageous to projectors of other types in terms of miniaturization. At present, portable compact projectors have spread widely, including a data projector convenient for presentation. It is important to reduce the thickness of a projector intended for portability, especially so if it is carried around often along with a notebook computer.
In order to solve this problem, JP 2004-271668, for example, discloses a method of designing a compact projection lens. In this example, when a 0.7 inch DMD is used, the effective aperture of the foremost lens of the zoom lens system is in the range of 39-42 mm and at least the thickness of the projector, however, cannot be reduced beyond 50 mm. This thickness is not sufficiently satisfactory when the projector is actually carried around, for example, along with a notebook personal computer.
It is therefore an object of the present invention to provide a compact small-aperture lens system which is suitable for the characteristics of a light bulb which changes a reflective direction of light from a light bulb such as the DMD, thereby forming an image, and which has high imageability of an enlarged image projected from the light bulb on a screen or a wall. Another object of the present is to provide a thin, portable, compact, light, high-quality projector which is capable of projecting a large image even in a limited space such as a small meeting room.